Kinzo

1. Overview

Most messengers send everything through a company’s servers. Kinzo has none. When two devices running Kinzo are on the same network, each can see the other; you pair them once, and from then on they exchange text, photos, videos, audio and voice notes directly, over a connection encrypted between the two of them.

That makes it useful exactly where ordinary messengers are not: at home when the internet is down but the router is still up, in workshops, warehouses, basements and boats with no signal, in classrooms and offices that would rather not pass files through the cloud, and anywhere a connection is slow or metered.

2. Getting started

Install Kinzo from Google Play on every device you want to reach — it talks to other devices running Kinzo.

• Android 8.0 or later
• Free, with no ads, no account and no sign-up
• All devices on Kinzo 1.2 or newer — connections have been encrypted since 1.2, and it does not talk to older versions

First run

The first time it opens, Kinzo shows a Welcome to Kinzo box — the same one you will later find as Settings. The one thing worth deciding here is Advertise my device as: the name other devices will see. It starts as your phone’s own name; change it to something like “My Phone” if you would rather the real name stayed private. Tap Save.

Android will also ask to allow notifications, which is how you hear about new messages and pair requests when Kinzo is not on screen. The camera and microphone are only asked for the first time you use them.

Two phones talking, in a minute

1. Put both phones on the same Wi-Fi and open Kinzo on both.
2. On one, open Available. The other phone appears under Kinzo devices on your network.
3. Tap Pair beside it.
4. On the other phone, check the six-digit code matches and tap Accept.
5. The device now appears under Trusted. Tap it and start typing.

3. The main screen

The bar at the top carries the Kinzo mark, with the name this device is advertising beneath it, a refresh button that looks for devices again, and the Settings gear. Below it are three tabs:

A small number on a tab is a count: trusted devices connected right now, devices found on the network, and unread messages.

4. Finding devices

Open Available. At the top is the This device card, with your advertised name and this phone’s address on the network (for example 192.168.1.19:47800). Under it, Kinzo devices on your network lists every device Kinzo has found, each with its address and a Pair button.

You do not have to do anything for this list to fill — devices announce themselves and turn up within a few seconds. A device that leaves the network, is switched off or closes Kinzo drops off again, so the list reflects what you can actually reach.

When nothing appears

The tab says Looking for Kinzo devices… and then tells you something useful: “This device is on 192.168.1.x”. Compare that with the address on the other phone’s own This device card. If the numbers do not start the same way, the two phones are on separate networks — usually a Wi-Fi extender or a guest network — and that, not Kinzo, is why they cannot find each other.

• Scan this network looks for Kinzo devices directly, for routers that filter the announcements devices normally find each other by. The refresh button at the top does the same.
• A QR code or Connect by IP reaches a device you can get to but cannot see — see the next sections.

5. Pairing

Pairing is how two devices agree to talk. Until both sides have said yes, nothing can be sent in either direction.

1. On the Available tab, tap Pair beside the device. The button changes to Waiting… and Kinzo confirms the request was sent.
2. The other device shows Pair with name? — in the app, or as a notification if Kinzo is in the background — with Decline and Accept.
3. Once it is accepted, each device appears in the other’s Trusted list.

The six-digit code

A pair request shows a six-digit number with the line Check this matches the other device. Both phones work the number out from both devices’ keys, so they show the same number when they are genuinely talking to each other. If something were sitting between them pretending to be each to the other, the two numbers would differ. Glance at both screens before tapping Accept — if they do not match, decline.

6. Pairing by QR code

A QR code gets two phones connected without either having to find the other first — the answer when a router blocks discovery, and the quickest way when the two of you are standing together.

On the phone to be scanned

Open Available and double-tap the This device card, or tap the QR button on it. A full-screen code appears with your device name and address. Tap Done when you are finished.

On the phone that scans

1. Open Available and tap Connect by IP.
2. Tap Scan QR code and allow the camera if asked.
3. Point it at the code. Kinzo reads it at any angle, fills in the address and connects.

The code carries every address the device has, and Kinzo tries each in turn, so a phone that is on both Wi-Fi and mobile data only needs the reachable one to answer. It also carries the device’s key: Kinzo checks the key before it connects, and if whatever answers is not the device whose code you scanned, nothing is connected and it says so.

7. Connect by IP

On the Available tab, Connect by IP reaches a device by its address. Enter the IP address shown on the other phone’s This device card and, if it is different from the default, the Port (the number after the colon — normally 47800), then tap Connect.

If a Kinzo device answers, it appears and you can pair as usual. If nothing does, Kinzo says that no Kinzo device answered at that address — check that the other phone has Kinzo open, that the address is typed exactly, and that the two phones can reach each other at all (see Troubleshooting).

8. Trusted devices

The Trusted tab lists every device you have paired with, each with its picture (or initials) and its state: Connected, or Offline with when it was last seen. A green dot on the picture means connected. Kinzo reconnects to trusted devices by itself whenever they are on the network — there is nothing to tap.

Tap a device to open its chat. The ⋮ menu on its row (or a long-press) offers:

• Message — open the chat, the same as tapping the row.
• Rename — give the device your own name for it. Only you see this name; it stays on your phone and is used in the Trusted list, Chats, the chat header and notifications. The name the device shares still shows in small print. Leave the box empty to go back to the shared name.
• Remove device — end the pairing. You will no longer exchange messages with that device until you pair again. Chat history is kept; deleting it is a separate step (see The Chats tab).

Removing a device also forgets its key and deletes its profile picture from your phone, and yours from theirs. To talk again, pair again from the Available tab — a removed device’s chat shows Not paired and says so.

9. Chatting

Open a chat from the Trusted or Chats tab. The header shows the device’s picture and name with its state beneath — Connected, Offline or Not paired. Type in the Message box and send.

What the ticks mean

When the other device is away

You can keep writing. The chat shows Offline — messages will be delivered when name is back on the network, and everything you send is queued. The moment the device reconnects, the queue is delivered — and a message is never delivered twice, even if the connection dropped half-way through.

Long-press a message

• Copy text — put a text message on the clipboard.
• Retry now — on a message marked as waiting to resend, try again at once instead of waiting for the next reconnect.
• Delete for me — remove the message from this device. The other device keeps its copy.

10. Photos, videos, audio & voice notes

Tap the + beside the message box for the Send sheet:

Kinzo has no storage or photo permission. The picker belongs to Android and hands Kinzo only the file you chose — it never sees the rest of your gallery. Camera and Record ask for the camera permission the first time.

Large files are sent in pieces with a progress bar on the message, on both devices. If the connection drops while a file is arriving, it is marked Interrupted on the receiving device, and the sender’s Kinzo sends it again when the two reconnect.

Voice notes

Tap the microphone at the end of the message box. Kinzo starts recording and shows the running time; tap send to send the note or the ✕ to throw it away. The first time, Android asks for the microphone permission. A voice note or audio file plays in the conversation — tap it to play or pause.

The viewer

Tap a photo or video in a chat to open it full-screen. Photos can be pinched to zoom. Share or save at the top hands the file to any other app on your phone — your gallery, a file manager, another messenger.

11. The Chats tab

Chats lists your conversations with the most recent first: the device’s picture and name, a preview of the last message (photos, videos and audio are named as such, and your own messages start with You:), its time, and a badge counting unread messages. Tap one to open it.

Long-press a conversation to delete it. Kinzo asks first, and is clear about the scope: messages and media are deleted from this device only. The other device keeps its copy, and the device stays paired — deleting a chat and removing a device are separate things.

12. Settings

The gear at the top right opens Settings. There are three parts; tap Save to keep your changes.

Profile picture

Choose (or Change) picks a picture with Android’s picker; Remove goes back to initials. The picture is shared only with devices you have paired with — a device that merely sees you under Available gets no picture. It appears beside your name on their Trusted list, Chats list and chat header, and they see a change the next time you connect.

Privacy

Advertise my device as is the name nearby devices see. The line under the box tells you whether that is your phone’s real name or not. Change it to anything you like; devices you are already paired with pick the new name up.

Background

Receive in background keeps Kinzo reachable when the app is closed, so messages and pair requests still arrive. Android requires an app that does this to show a permanent notification while it runs. Switch it off and Kinzo only receives while it is open; anything sent to you in the meantime waits on the sender’s device and arrives when you next open the app.

13. Security & privacy

• Connections are encrypted with TLS, device to device. There is no server between the two devices, so there is nothing in the middle that could read or keep your messages.
• Every device has its own key, created when Kinzo is installed. Pairing records the other device’s key, and every later connection must present it. A device presenting a different key is refused, and Kinzo tells you it presented a different security key.
• A device cannot borrow another’s name. Identity is tied to the key, so something on the network announcing itself as a device you trust gets nowhere without that device’s key.
• The six-digit code at pairing and the key check when scanning a QR code are how you confirm the first connection is with the device you meant.
• No account, no sign-up, no phone number, no email. We run no servers and collect nothing; there is no analytics and there are no ads.
• Mobile data is never used for messaging.

14. Permissions

Kinzo asks for no storage, photo, contacts or location permission. Decline the camera or microphone and everything else keeps working — you just cannot use the feature that needs it.

15. Troubleshooting

• The other phone does not appear under Available. Check, in this order: Kinzo is open on it (or Receive in background is on); both phones are on the same Wi-Fi name; and the addresses on the two This device cards start with the same numbers. Then tap refresh or Scan this network.
• The addresses start differently (say 192.168.1.x on one and 192.168.11.x on the other). The phones are on separate networks. The usual culprit is a Wi-Fi extender running as its own router — its network name often ends in “-EXT” — or a guest network. Put both phones on the same network name.
• Same network, still nothing. Some routers stop devices seeing each other’s announcements. Use a QR code or Connect by IP.
• Even Connect by IP gets no answer. The router has client isolation switched on (common on guest, hotel and café Wi-Fi), which stops devices on it talking to each other at all. No app can get around that on that network. Turning on one phone’s Wi-Fi hotspot and joining it from the other gives the two a network of their own.
• “That device needs Kinzo 1.2 or newer.” Update Kinzo on the other device from Google Play.
• A trusted device shows Offline although it is right here. It may have Kinzo closed with Receive in background off, or have joined a different network. Open Kinzo on it; it reconnects by itself within a few seconds.
• A device is refused for presenting a different security key. Kinzo was reinstalled or its data cleared on that device, so it has a new key. If you are sure it is the same device, Remove device on the Trusted tab and pair again — your chat history is kept.
• My message has stayed on one tick. The other device has not confirmed it yet — it is probably off the network. It is delivered when the device returns, with nothing for you to do. A message showing the warning mark instead can be long-pressed for Retry now.
• Messages only arrive when I open the app. Switch on Settings → Receive in background, and check that Android’s battery settings are not restricting Kinzo.
• The camera or microphone button says a permission is needed. Allow it in Android’s Settings → Apps → Kinzo → Permissions.